Russian troops could invade Ukraine within 12 hours of getting an order, General Philip Breedlove, NATO’s Supreme Allied Commander Europe, told CNN’s Christiane Amanpour on Wednesday.

“It’s my opinion that they could move within 12 hours of a go,” General Breedlove said from NATO headquarters in Brussels. “So essentially they could move right away if given the go.”

General Breedlove said that there are now 40,000 Russian troops massed on Ukraine’s eastern border.

But even that number, he said, doesn’t tell the full story.

“This is a combined-arms army, with all of the pieces necessary should there be a choice to make an incursion into Ukraine,” he said.

Forces are “supported by fixed-wing aircraft [airplanes], rotary aircraft [helicopters] – all of the logistics required in order to successfully make an incursion if they needed.”

NATO announced on Tuesday that it will suspend "all practical civilian and military cooperation" with Russia because of its annexation of Crimea.

Ukraine is not a NATO member, but many countries that are members – such Poland and the Baltic states – have voiced their increasing anxiety about Russia’s recent actions.

General Breedlove said that he is preparing strong options to deter further moves by Russian President Valdimir Putin, including ground forces.